1. Technical Field
The present disclosure relates to an asymmetrically changing rotating propeller and, more specifically, to an asymmetrically changing rotating blade shape propeller and its airplane and wind turbine applications.
2. Description of the Related Art
A propeller is a device which forces fluid passing through it and increases the fluid kinetic energy. Vehicles or vessels such as airplanes, ships and submarines may use propellers to propel though a fluid such as air or water. Alternatively, a propeller can be placed in the path of a moving fluid to absorb the fluid kinetic energy, such as a wind mill. A typical propeller is generally comprised of one or more twisted blades which are rotated around a central shaft.
Conventional propellers have an identical geometric configuration that remains constant as the blades revolve around the central shaft. Both lift and drag force components are developed on the blade. Only the fluid momentum increase in the axial direction is utilized to produce desired axial thrust.
While conventional propellers provide symmetric thrust with respect to each revolution cycle, examples of asymmetric propulsion techniques are known. For example, when rowing a rowboat, a boater sweeps an oar from front to back while its face is submerged in water and then, to complete the rowing cycle, the boater carries the oar to its original front position while removed from the water. By moving the oar from the more dense water to the less dense air on the return stroke, the boater is able to apply maximum energy during the front-to-back sweep and conserve energy on the return thereby maximizing propulsion efficiency. The angle of the oar may also be adjusted by the boater to further optimize propulsion efficiency
Another example is when a swimmer performs the breast-stroke. Here a swimmer's arms are swept from front-to-back while under the water and are then returned to their original front position while removed from the water. The angle of the swimmer's hands may also be adjusted to optimize the propulsion efficiency.
In this way, the boater and swimmer are able to adjust the coefficient of drag of the oar/arm so that the drag is higher where it is needed the most and lower where it is needed the least. However, conventional propellers are unable to adjust their coefficient of drag during the blade's cycle of rotation and thus propulsion cannot be optimized.
Some propellers in the art have the ability to change blade pitch to improve propeller performance. For example, U.S. Pat. No. 6,991,426, to Pietricola, and U.S. Pat. No. 6,942,458, to McCallum et al., describe variable pitch propellers where blade pitch is adjusted according to the needs of the airplane. For example, the blades may have one pitch during takeoff and another pitch during high-altitude cruise.
While such variable pitch propellers have the ability to alter blade lift and drag coefficients, lift and drag are not changed during the course of the propeller's rotational cycle. Another example involved the wing flapping of a bird or an insect. In the first half of a wing-flapping cycle, the wing pushes the air downward/backward of the bird. This increases downward/backward air momentum passing through the wing. The reaction to this air momentum increase is a force which pushes the bird upward/forward. Next, the wing must return to its starting cycle configuration in order to be ready for its next wing-flapping cycle. This is done during the second half of the wing-flapping cycle. Most wings are not designed to produce desired thrust in both half cycles. Therefore, the wing must conserve its energy to perform its second half cycle return journey.
Accordingly, it is desired that a propeller have the ability to adjust the drag coefficient of each blade during the course of the propeller's rotational cycle.